Synchronizer and method for shifting a gear

ABSTRACT

A method for shifting a gear in a synchronizer comprising a synchronizer body arranged on a transmission shaft, a first and a second synchronizer associated to a first and a second transmission gear, wherein the synchronizer has a sliding sleeve and at least one thrust piece which is shiftably arranged on the synchronizer body and can exert an axial compressive force on the corresponding synchronizer ring. The synchronizer includes an elastic actuating element active between the sliding sleeve and the thrust piece, and the sliding sleeve has a detent recess for the neutral position and a release contour that can cooperate with the actuating element such that when the sliding sleeve is shifted for being engaged with one of the transmission gears, the thrust piece is urged away from the corresponding synchronizer ring.

This invention relates to a synchronizer for a gear transmission and toa method for shifting a gear in a synchronizer.

BACKGROUND OF THE INVENTION

From the prior art synchronizers are known, which include a synchronizerbody associated to a transmission shaft. On the synchronizer body athrust piece typically is shiftably arranged, which during a shiftingoperation is moved by a sliding sleeve such that it activates asynchronizer ring. The synchronizer ring in turn cooperates with atransmission gear, whereby the rotational speeds of the synchronizerbody and of the corresponding transmission gear can be synchronized.After synchronization of the rotational speeds, the sliding sleeve isshifted further so that a torque can be transmitted from thesynchronizer body arranged on the transmission shaft to thecorresponding transmission gear.

It was found that on meshing of the sliding sleeve on the transmissiongear, the synchronizer ring continues to be axially loaded by the thrustpiece such that a friction moment is obtained, which must be overcome onmeshing. The cause for the further axial loading of the synchronizerring by the thrust piece chiefly is the friction between the thrustpiece and the synchronizer body on which the thrust piece is arranged.Due to the friction between the thrust piece and the synchronizer bodyan axial return movement of the thrust piece is prevented. Thedisadvantage consists in that when engaging a gear, an increasedexpenditure of force is necessary in order to overcome the frictionalforce generated by the synchronizer ring via the thrust piece. Thisproblem occurs in particular when a vehicle is stationary.

It therefore is the object of the invention to create a synchronizerwhich provides for smoothly engaging the gear.

SUMMARY OF THE INVENTION

According to the invention this object is solved by a synchronizer for agear transmission, comprising a synchronizer body which is associated toa transmission shaft, a first and a second synchronizer ring which areassociated to a first and a second transmission gear and during ashifting operation can synchronize the rotational speeds of thesynchronizer body and the corresponding transmission gear, a slidingsleeve which is non-rotatably arranged on the synchronizer body and canbe shifted from a neutral position in opposite directions into a firstand a second shifting position in order to non-rotatably couple thefirst and the second transmission gear with the synchronizer body, andat least one thrust piece which is shiftably arranged on thesynchronizer body and during a shifting operating can exert an axialcompressive force on the corresponding synchronizer ring, wherein anelastic actuating element is provided, which is active between thesliding sleeve and the thrust piece, wherein a detent recess for theneutral position as well as a release contour are provided on thesliding sleeve, wherein the release contour can cooperate with theactuating element such that when the sliding sleeve is shifted for beingengaged with one of the transmission gears, the thrust piece is urgedaway from the corresponding synchronizer ring, and wherein the releasecontour has an axial length which is not more than twice the idle strokeof the sliding sleeve between the neutral position and the position inwhich the corresponding synchronizer ring presses against an associatedfriction surface.

The idea underlying the invention consists in dividing the pressingoperation of the thrust piece into two portions: in a first portion thethrust piece is pressed against the synchronizer ring so that thefriction moment required for the pre-synchronization is generated, andin a second portion the thrust piece is actively released so that thesynchronizer ring no longer is pressurized. As a result, no frictionoccurs in the friction package consisting of the synchronizer ring andthe corresponding transmission gear. Furthermore, an increasedsynchronizer capacity can be achieved with the synchronizer according tothe invention, as smaller cone angles can be used. The length of therelease contour is designed such that when releasing the frictionpackage, the opposed friction package is not loaded so that no unwantedfriction occurs there.

In particular, the actuating element includes a spring which is arrangedon the thrust piece. Via the spring, the elasticity of the actuatingelement is provided such that the actuating element can slide along therelease contour and the detent recess of the sliding sleeve.

One aspect of the invention provides that the actuating elementcomprises a ball which in the neutral position is urged into the detentrecess of the sliding sleeve by the spring. The formation of theactuating element as a ball pressurized by a spring ensures that thesliding sleeve is held in the neutral position due to its detent recess.As a result, a force overcoming the spring force is required, in orderto trigger the shifting operation.

A further aspect of the invention provides that the release contour isadjoined by a protrusion on the side associated to the detent recess andby a holding portion on the opposite side. The protrusion defines thepoint from which during shifting the actuating element transitions fromthe detent recess into the release contour, whereby the point is definedat which the thrust piece is moved back and releasing of the frictionpackage starts. The holding portion adjoins the release contour, whereinthe holding portion is designed such that releasing of the frictionpackage is maintained and in addition the other friction package is notloaded.

In particular, the center of the protrusion has an axial distance to thecenter of the detent recess which is smaller than the axial shiftingpath of the sliding sleeve which is covered in order to transmit atorque from the synchronizer body to one of the transmission gears. Thedistance in particular is smaller than the axial shifting path of thesliding sleeve minus the distance which is covered by the thrust piecefrom the neutral position until abutment against the correspondingsynchronizer ring. It thereby is achieved that the friction package tobe released already is released at the beginning of meshing, so thatsmooth meshing is possible.

A further aspect of the invention provides that the release contourincludes an angle α to the axial alignment of the synchronizer, whichlies between 10° and 40°, in particular is 25°. Via the angle α, theaxial force is adjusted which acts on the thrust piece from the releasecontour via the actuating element, whereby the thrust piece can beshifted axially and the friction package is released correspondingly. Ifthe angle assumed was too small a value, the axial force would not besufficient to correspondingly axially shift the thrust piece.

According to one aspect of the invention, the first and the secondsynchronizer ring each are formed cone-shaped. Via the cone-shapedformation, increased friction values can be achieved. It generally ispossible with such synchronizer rings to provide single-cone ordouble-cone synchronizers.

In particular, one cone-shaped intermediate ring as well as twocone-shaped synchronizer rings are provided per transmission gear,between which synchronizer rings the intermediate ring is arranged sothat a triple-cone synchronizer is formed. A triple-cone synchronizer isadvantageous because particularly high friction values can be achievedwhereby a correspondingly fast synchronization of the rotational speedsis achievable. The friction package accordingly is formed by theintermediate ring, the two synchronizer rings and the associatedtransmission gear.

A further aspect of the invention provides that the side of the slidingsleeve associated to the synchronizer body is formed mirror-symmetricalwith respect to its vertical middle axis. This means that pertransmission gear one release contour each is provided whereby it ispossible to actively shift the thrust piece on meshing of the slidingsleeve in both gears or transmission gears in order to relieve orrelease the corresponding friction packages.

Furthermore, the invention relates to a method for shifting a gear in asynchronizer with a synchronizer body which is associated to atransmission shaft, a first and a second synchronizer ring which areassociated to a first and a second transmission gear and during ashifting operation can synchronize the rotational speeds of thesynchronizer body and the corresponding transmission gear, a slidingsleeve which is non-rotatably arranged on the synchronizer body and froma neutral position can be shifted in opposite directions into a firstand a second shifting position, in order to non-rotatably couple thefirst and the second transmission gear with the synchronizer body, andat least one thrust piece which is shiftably arranged on thesynchronizer body and during a shifting operation can exert an axialcompressive force on the corresponding synchronizer ring, wherein anelastic actuating element is provided which is active between thesliding sleeve and the thrust piece, comprising the following steps:

a) axially shifting the sliding sleeve from a neutral position to ashifting position,

b) pressing the thrust piece rotating with the synchronizer body againstthe synchronizer ring associated to the transmission gear forpre-synchronization,

c) synchronizing the rotational speed of the synchronizer body and thecorresponding synchronizer ring with that of the transmission gear,

d) further axial shifting of the sliding sleeve to the shifting positionafter completed synchronization,

e) exerting an axial force pointing away from the correspondingtransmission gear on the thrust piece, in particular on the actuatingelement, by the release contour of the sliding sleeve during furtheraxial shifting so that the thrust piece no longer rests or is pressedagainst the corresponding synchronizer ring, and

f) reaching of the shifting position, wherein the actuating element nolonger rests against the release contour.

By the method according to the invention the advantages mentionedalready for the synchronizer are achieved, according to which thefriction package is released on meshing of the sliding sleeve and aftercompleted synchronization so that meshing takes place correspondinglysmoothly.

In particular, the exerted axial force is greater than the frictionalforce between the thrust piece and the synchronizer body. Due to thisforce ratio, the axial compressive force exerted by the release contouron the actuating element and thus on the thrust piece can overcome thestatic friction between thrust piece and synchronizer body so that thefriction package is actively released.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages and properties of the invention can be taken from thefollowing description and the following drawings to which reference ismade. In the drawings:

FIG. 1 shows a partial cross-section of a synchronizer according to theinvention with two transmission gears associated to the same, whereinthe synchronizer is in a neutral position,

FIG. 2 shows a detail view of FIG. 1,

FIG. 3 shows the synchronizer of FIG. 1 in a pre-synchronizing position,

FIG. 4 shows the synchronizer of the previous Figures in a blockingposition,

FIG. 5 shows the synchronizer of the previous Figures at a point in timeat the end of the blocking position,

FIG. 6 shows the synchronizer of the previous Figures at the beginningof meshing,

FIG. 7 shows the synchronizer of the previous Figures at a later pointin time of meshing, and

FIG. 8 shows the synchronizer of the previous Figures after completedshifting.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a synchronizer 10 which includes a synchronizer body 12which via a toothing 14 is non-rotatably arranged on a non-illustratedtransmission shaft. The transmission shaft rotates about an axis whichin FIG. 1 lies horizontally below the toothing 14.

The synchronizer body 12 includes a hub portion 16 in which a thrustpiece 18 is shiftably arranged. To the thrust piece 18 an actuatingelement 20 is associated, which in the embodiment shown is formed by aball 22 and a spring 24. The spring 24 supports on the thrust piece 18and urges the ball 22 in direction of a sliding sleeve 26, i.e. radiallyto the outside.

The sliding sleeve 26 is non-rotatably connected with the synchronizerbody 12 and can axially be shifted in opposite directions in order tocouple the synchronizer body 12 with a first transmission gear 28 or asecond transmission gear 30, whereby a torque can be transmitted fromthe transmission shaft to the corresponding transmission gear 28, 30.The two transmission gears 28, 30 are arranged on the transmission shaftbut can freely rotate on the same unless they are non-rotatablyconnected to the transmission shaft via the sliding sleeve 26 to thesynchronizer body 12 which in turn is non-rotatably connected to thetransmission shaft via the toothing 14.

For pre-synchronizing the rotational speeds of the transmission gear 28,30 and the synchronizer body 12, the synchronizer 10 in the embodimentshown includes a synchronizer ring formed as blocking ring 32, 36, asynchronizer ring 34, 38 as well as an intermediate ring 40, 42 for eachtransmission gear 28, 30. The blocking rings 32, 36 are non-rotatablyconnected with the synchronizer body 12. Each of the synchronizer rings34, 38 is non-rotatably connected with the corresponding blocking ring32, 36. Each of the intermediate ring 40, 42 is non-rotatably connectedwith the associated transmission gear 28, 30. Thus, the two intermediaterings 40, 42 rotate with the rotational speed of the correspondingtransmission gear 28, 30, while the blocking rings 32, 36 and thesynchronizer rings 34, 38 rotate with the rotational speed of thesynchronizer body 12.

The blocking rings 32, 36, the synchronizer rings 34, 38 and theintermediate rings 40, 42 all are formed cone-shaped. The contactsurfaces between transmission gear and synchronizer ring, betweensynchronizer ring and intermediate ring as well as between intermediatering and blocking ring each are formed as friction surface of atriple-cone synchronizer with a friction lining and within a frictionpackage 44, 46, with which the torque required for synchronizingtransmission gear 28, 30 and synchronizer body 12 can be generated.

The sliding sleeve 26 has a side 48 associated to the thrust piece 18,which cooperates with the actuating element 20. On this side 48, thesliding sleeve 26 has a detent recess 50 in which the ball 22 of theactuating element 20 is pressurized by the spring 24 in the neutralposition of the synchronizer 10. Adjacent to the detent recess 50 aprotrusion 52 is formed which is adjoined by a release contour 54 and aholding portion 56 (see FIG. 2).

Relative to the axial alignment A of the synchronizer 10, the releasecontour 54 is formed inclined by an angle α, wherein it extends linearlyin general. Furthermore, the release contour 54 maximally extends alongan axial length which corresponds to twice the distance covered by thesliding sleeve 26 until the thrust piece 18 rests against the blockingring 32. This distance also is referred to as idle stroke orpre-synchronizing path of the sliding sleeve 26.

In the embodiment shown, the holding portion 56 is formed parallel tothe axial alignment A of the synchronizer 10 and extends in axialdirection up to the end of the sliding sleeve 26, which is associated tothe other blocking ring 36.

The mode of operation of the synchronizer 10 and in particular of therelease contour 54 as well as of the entire side 48 of the slidingsleeve 26 associated to the thrust piece 18 can be taken from thefollowing description, which describes the course of shifting proceedingfrom the neutral position of the synchronizer 10 as shown in FIG. 1 to afinal shifting position of the synchronizer 10 as shown in FIG. 8.

FIG. 3 shows the synchronizer 10 of FIG. 1, wherein the sliding sleeve26 has been shifted axially to the first transmission gear 28 relativeto the condition of FIG. 1 and via the detent recess 50 has entrainedthe ball 22 of the actuating element 20 so that the thrust piece 18 alsois axially shifted within the synchronizer body 12 towards the firsttransmission gear 28.

Since the thrust piece 18 is axially shifted, the thrust piece 18 restsagainst the first blocking ring 32 such that the first friction package44 is loaded. The thrust piece 18 effects indexing of the blocking ring32 and the sliding sleeve 26. Furthermore, the process of synchronizingthe rotational speed of the transmission gear 28 with the rotationalspeed of the synchronizer body 12 thereby is started.

FIG. 4 shows the synchronizer 10 at a later point in time, wherein thesynchronizer 10 is in a blocking position. Due to the acting torquebetween the synchronizer body 12 and the transmission gear 28, theblocking ring 32 is rotated with respect to the synchronizer body 12 tosuch an extent that external blocking teeth 58 of the internal toothingof the sliding sleeve 26 are opposed to the internal toothing (moreexactly the tips 60 of the internal toothing) such that the slidingsleeve 26 cannot be shifted further axially.

When the sliding sleeve 26 is in the blocking position, the ball 22still is arranged in the region of the detent recess 50 of the slidingsleeve 26, so that the center of the actuating element 20 as shown inthe drawing axially is closer to the first transmission gear 28 than thecenter of the protrusion 52.

FIG. 5 shows the synchronizer 10 in a condition in which the slidingsleeve 26 has been shifted beyond the blocking position in axialdirection towards the transmission gear 28. By cooperation of theblocking teeth 58 and the tips 60, the sliding sleeve 26 therefore hasrotated the blocking ring 32 out of its blocking position such that theblocking teeth 58 of the blocking ring 32 no longer lie before the tips60 of the sliding sleeve 26. This was possible as soon as the rotationalspeeds of transmission gear 28 and synchronizer body 12 have beensynchronized sufficiently so that the synchronizing torque acting on theblocking ring 32 collapses.

In the condition of FIG. 5, the sliding sleeve 26 is not yet coupledwith the first transmission gear 28 as there can still be seen a gapbetween sliding sleeve 26 and first transmission gear 28. This conditionalso is referred to as free-flight phase since at this time the slidingsleeve 26 is in engagement neither with the first blocking ring 32 norwith the first transmission gear 28.

In this condition, the protrusion 52 of the sliding sleeve 26furthermore still is axially further away from the first transmissiongear 28 than the middle of the actuating element 20 as shown in theFigure.

The thrust piece 18 also continues to rest against the first blockingring 32 whereby the thrust piece 18 axially pressurizes the firstblocking ring 32, and the first friction package 44 is loaded.

FIG. 6 shows the synchronizer 10 at the beginning of meshing of thesliding sleeve 26 into the first transmission gear 28. The condition ofmeshing is defined in that the toothing-like tips 60 of the slidingsleeve 26 just get in contact with toothing-like tips 62 of the firsttransmission gear 28. In terms of alignment, the tips 62 of the firsttransmission gear 28 are formed analogous to the blocking teeth 58 ofthe first blocking ring 32.

In this condition, the beginning of meshing, the ball 22 of theactuating element 20 tangentially rests against the protrusion 52 of thesliding sleeve 26 so that the ball 22 is in an unstable equilibrium,i.e. at the dead center. This means that at the meshing point the ball22 centrally rests against the protrusion 52 exactly between the detentrecess 50 and the release contour 54.

The thrust piece 18 continues to axially rest against the first blockingring 32 and correspondingly pressurizes the first friction package 44.

FIG. 7 shows the synchronizer 10 at a later point in time, wherein thesliding sleeve 26 has been moved minimally with respect to the positionof FIG. 6, so that the ball 22 has been brought out of the unstableequilibrium.

The ball 22 has slipped over the protrusion 52 and is pressurized by thespring 24 along the release contour 54. Due to the oblique alignment bythe angle α, the release contour 54 generates an axial force on the ball22 and the actuating element 20, which in turn is axially pressurized bythe thrust piece 18. The thrust piece 18 ultimately is urged away fromthe first transmission gear 28, whereby the first friction package 44 isdisengaged or release.

Due to the relief of the first friction package 44, the sliding sleeve26 can be meshed more smoothly in order to couple with the firsttransmission gear 28, as no friction moment must be overcome between thesynchronizer body 12 and the transmission gear 28.

The angle α of the release contour 54 typically lies between 10° and40°, in particular is 25°, so that the axial force exerted by therelease contour 54 is large enough to overcome the frictional forcebetween the thrust piece 18 and the hub portion 16 of the synchronizerbody 12, so that the thrust piece 18 can axially be shifted at all.

The complete shifting of the gear is shown in FIG. 8, wherein thesliding sleeve 26 is coupled into the first transmission gear 28 withthe synchronizer body 12, so that a torque can be transmitted from thetransmission shaft via the synchronizer body 12 to the firsttransmission gear 28.

In this condition, the ball 22 rests against the sliding sleeve 26 inthe region of a holding portion 56 on the side 48 associated to thethrust piece 18. It thereby is achieved that the axial compressive forceexerted on the actuating element 20 is not so large that the thrustpiece 18 is urged away from the first transmission gear 28 too far. Ifthis would be the case, the thrust piece 18 might axially pressurize theblocking ring 36 opposite to the first blocking ring 32, whereby thesecond friction package 46 would be loaded. The axial length of therelease contour 54 therefore maximally is as long as twice the idlestroke of the sliding sleeve 26, as already mentioned above.

The course of the holding portion 56 can be formed parallel to the axialalignment A of the synchronizer 10, as shown here, or with a smallpositive or negative angle. The holding portion 56 however should beformed such that the axial force acting on the ball 22 is small. Theforce should be so small that the thrust piece 18 does not get incontact with the opposite blocking ring 36 and the second frictionpackage 46 would be loaded.

The shown embodiment of the synchronizer 10 merely has one releasecontour 54 on the sliding sleeve 26. However, there can also be provideda sliding sleeve 26 which on both sides of the detent recess 50 eachincludes a protrusion and a release contour along with a holdingportion, whereby releasing both friction packages 44, 46 is possiblewhen shifting both gears. Such sliding sleeve 26 is characterized by itsmirror symmetry on the side 48.

What is claimed is:
 1. A method for shifting a gear in a synchronizercomprising a synchronizer body arranged on a transmission shaft, a firstand a second synchronizer ring proximate to a first and a secondtransmission gear, which first and second synchronizer ring cansynchronize rotational speeds of the synchronizer body and an adjacenttransmission gear during a shifting operation, a sliding sleeve which isnon-rotatably arranged on the synchronizer body and which sleeve can beshifted from a neutral position in opposite directions into a first anda second shifting position to non-rotatably couple the first and thesecond transmission gear with the synchronizer body, a detent recess forthe neutral position as well as a release contour are provided on thesliding sleeve, and at least one thrust piece shiftably arranged on thesynchronizer body which during a shifting operation can exert an axialcompressive force on the synchronizer ring corresponding to thetransmission gear for pre-synchronization, wherein an elastic actuatingelement is provided which is active between the sliding sleeve and thethrust piece, comprising steps: a) axially shifting the sliding sleevefrom a neutral position to a shifting position, b) pressing the thrustpiece rotating with the synchronizer body against the synchronizer ringcorresponding with the transmission gear for pre-synchronization, c)synchronizing the rotational speeds of the synchronizer body, thesynchronizer ring of b) and the transmission gear, d) further axialshifting of the sliding sleeve to the shifting position after completedsynchronization, e) exerting an axial force pointing away from thecorresponding transmission gear on the thrust piece, by the releasecontour of the sliding sleeve through the actuating element duringfurther axial shifting so that the thrust piece no longer rests or ispressed against the corresponding synchronizer ring, and f) reaching ofthe shifting position, wherein the actuating element no longer restsagainst the release contour.
 2. The method according to claim 1,characterized in that the exerted axial force is greater than frictionalforces between the thrust piece and the synchronizer body.
 3. The methodaccording to claim 1 wherein the actuating element is arranged on thethrust piece via a spring.
 4. The method according to claim 3, whereinthe actuating element comprises a ball which in the neutral position isurged into the detent recess of the sliding sleeve by the spring.
 5. Themethod according to claim 1, wherein the release contour is adjoined bya protrusion on the side associated to the detent recess and by aholding portion on the opposite side.
 6. The method according to claim5, wherein the center of the protrusion has an axial distance to thecenter of the detent recess which is smaller than the axial shiftingpath of the sliding sleeve that is covered, in order to transmit atorque from the synchronizer body to one of the transmission gears, inparticular is smaller than the axial shifting path of the sliding sleeveminus the distance covered by the thrust piece from the neutral positionup to the abutment against the corresponding synchronizer ring.
 7. Themethod according to claim 1 wherein the release contour includes anangle α to the axial alignment (A) of the synchronizer, which liesbetween 10° and 40°.
 8. The method according to claim 1, wherein thefirst and the second synchronizer ring each is formed cone-shaped, inparticular that per transmission gear a cone-shaped intermediate ringand two cone-shaped synchronizer rings are provided, between which theintermediate ring is arranged so that a triple-cone synchronizer isformed.
 9. The method according to claim 1 wherein the side of thesliding sleeve associated with the synchronizer body is formedmirror-symmetrical with respect to its vertical middle axis.